In the restaurant industry specifically and others generally, there is a need to clean contaminants from exhaust air generated by cooking or other processes prior to discharging the air to the atmosphere. Recent solutions for removing contaminants include high cost and frequently undependable electrostatic precipitators, energy consuming turbo-charged afterburners and large multi-station spray nozzle and baffle plate water scrubbers. The spray nozzle, baffle plate scrubber is generally the most economical of the three types, however, it has additional problems with inconsistent water flow caused by the clogging of spray nozzles by solids in the water; most types that depend on baffle plates have high air side pressure drops which like the pump systems for the spray nozzles require high energy consumption.
Examples of scrubber systems utilizing spray nozzles include U.S. Pat. No. 3,616,744 (Jensen) which describes an air cleaning system for cooking ranges that is adapted to remove heat and contaminants such as grease laden fumes. A stream of contaminant-laden air is drawn into an exhaust duct by an exhaust fan and cleansed by the washing action of minute water droplets from a fogging spray. The droplets absorb the contaminants and fall out into a water bath. Also, vaporization of the droplets cools the stream of exhaust air causing condensation of contaminants. Other systems utilizing spray nozzles are described in U.S. Pat. No. 3,624,696 (Cohen) and U.S. Pat. No. 3,731,462 (Costarella).
An older known method of purifying exhaust air consists of directing the airstream over a water reservoir causing water to be entrained in the airstream, then utilizing upstream baffles to cause the airstream to flow in a sinuous path causing the air and water to mix. In U.S. Pat. No. 266,267 (Breen), an air purifier is illustrated that directs an airstream against a surface of water at an angle so as to spray the water. Partitions are arranged in the subsequent path of the airstream so as to catch the water particles and drip them across the air passage. In U.S. Pat. Nos. 2,373,330 (Nutting) and 2,403,545 (Nutting), an air cleaner is disclosed having a water bath and an arrangement of baffles above the bath forming a sinuous path for the exhaust airstream. The exhaust air is intensively centrifuged and a substantially continuous stream of liquid from the bath is air-propelled along the sinuous path. With an S-shaped path, the air is twice centrifuged, twice scrubbed against a film of water and twice forced to pass through a curtain of water with the result that airborne particles are wetted and drop out of the exhaust airstream.
Other systems arrange the baffles in such a way that the incoming airstream is wetted both from above and below. For example, U.S. Pat. Nos. 2,379,795 (Fenn) and 2,470,345 (Fenn) disclose an exhaust airstream that is wetted by liquid in a reservoir area and is also wetted by liquid dripping from a baffle. A similar system is disclosed in U.S. Pat. No. 3,778,979 (Friedling) wherein the baffle above the incoming airstream has a gap that allows water-laden gas to be induced by venturi effect into the upper zone of the airstream passageway.
Other baffle systems utilize secondary sumps for collecting water entrained in the airstream. In U.S. Pat. No. 4,720,291 (London), a system is disclosed wherein water from the secondary sump is used to prewash the incoming airstream. U.S. Pat. No. 2,015,174 (Anglemyer) and U.S. Pat. No. 3,810,349 (Rebours) also illustrate secondary sumps that collect liquid dripping off the baffles and return the liquid to the primary sump or evacuate the liquid from the system.
The use of such sump and baffle systems may not always result in a sufficiently thorough mixing of contaminant-laden air and water. For example, portions of the airstream may totally bypass the water reservoir. Alternatively, water curtains created by inclined baffles may only develop intermittently or not along the full width of the scrubbing chamber allowing air to pass by the curtain area without contacting water. Because increased air/water contact results in better scrubbing action, it is of utmost importance that as much of the contaminant-laden air as possible come into contact with water.